/*
 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package javax.xml.transform.stax;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.events.XMLEvent;
import javax.xml.transform.Source;

/**
 * <p>Acts as a holder for an XML {@link Source} in the
 * form of a StAX reader,i.e.
 * {@link XMLStreamReader} or {@link XMLEventReader}.
 * <code>StAXSource</code> can be used in all cases that accept
 * a <code>Source</code>, e.g. {@link javax.xml.transform.Transformer},
 * {@link javax.xml.validation.Validator} which accept
 * <code>Source</code> as input.
 *
 * <p><code>StAXSource</code>s are consumed during processing
 * and are not reusable.</p>
 *
 * @author <a href="mailto:Neeraj.Bajaj@Sun.com">Neeraj Bajaj</a>
 * @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @see <a href="http://jcp.org/en/jsr/detail?id=173"> JSR 173: Streaming API for XML</a>
 * @see XMLStreamReader
 * @see XMLEventReader
 * @since 1.6
 */
public class StAXSource implements Source {

  /**
   * If {@link javax.xml.transform.TransformerFactory#getFeature(String name)}
   * returns true when passed this value as an argument,
   * the Transformer supports Source input of this type.
   */
  public static final String FEATURE =
      "http://javax.xml.transform.stax.StAXSource/feature";

  /**
   * <p><code>XMLEventReader</code> to be used for source input.</p>
   */
  private XMLEventReader xmlEventReader = null;

  /**
   * <p><code>XMLStreamReader</code> to be used for source input.</p>
   */
  private XMLStreamReader xmlStreamReader = null;

  /**
   * <p>System identifier of source input.</p>
   */
  private String systemId = null;

  /**
   * <p>Creates a new instance of a <code>StAXSource</code>
   * by supplying an {@link XMLEventReader}.</p>
   *
   * <p><code>XMLEventReader</code> must be a
   * non-<code>null</code> reference.</p>
   *
   * <p><code>XMLEventReader</code> must be in
   * {@link XMLStreamConstants#START_DOCUMENT} or
   * {@link XMLStreamConstants#START_ELEMENT} state.</p>
   *
   * @param xmlEventReader <code>XMLEventReader</code> used to create this <code>StAXSource</code>.
   * @throws XMLStreamException If <code>xmlEventReader</code> access throws an
   * <code>Exception</code>.
   * @throws IllegalArgumentException If <code>xmlEventReader</code> == <code>null</code>.
   * @throws IllegalStateException If <code>xmlEventReader</code> is not in
   * <code>XMLStreamConstants.START_DOCUMENT</code> or <code>XMLStreamConstants.START_ELEMENT</code>
   * state.
   */
  public StAXSource(final XMLEventReader xmlEventReader)
      throws XMLStreamException {

    if (xmlEventReader == null) {
      throw new IllegalArgumentException(
          "StAXSource(XMLEventReader) with XMLEventReader == null");
    }

    // TODO: This is ugly ...
    // there is no way to know the current position(event) of
    // XMLEventReader.  peek() is the only way to know the next event.
    // The next event on the input stream should be
    // XMLStreamConstants.START_DOCUMENT or
    // XMLStreamConstants.START_ELEMENT.
    XMLEvent event = xmlEventReader.peek();
    int eventType = event.getEventType();
    if (eventType != XMLStreamConstants.START_DOCUMENT
        && eventType != XMLStreamConstants.START_ELEMENT) {
      throw new IllegalStateException(
          "StAXSource(XMLEventReader) with XMLEventReader "
              + "not in XMLStreamConstants.START_DOCUMENT or "
              + "XMLStreamConstants.START_ELEMENT state");
    }

    this.xmlEventReader = xmlEventReader;
    systemId = event.getLocation().getSystemId();
  }

  /**
   * <p>Creates a new instance of a <code>StAXSource</code>
   * by supplying an {@link XMLStreamReader}.</p>
   *
   * <p><code>XMLStreamReader</code> must be a
   * non-<code>null</code> reference.</p>
   *
   * <p><code>XMLStreamReader</code> must be in
   * {@link XMLStreamConstants#START_DOCUMENT} or
   * {@link XMLStreamConstants#START_ELEMENT} state.</p>
   *
   * @param xmlStreamReader <code>XMLStreamReader</code> used to create this
   * <code>StAXSource</code>.
   * @throws IllegalArgumentException If <code>xmlStreamReader</code> == <code>null</code>.
   * @throws IllegalStateException If <code>xmlStreamReader</code> is not in
   * <code>XMLStreamConstants.START_DOCUMENT</code> or <code>XMLStreamConstants.START_ELEMENT</code>
   * state.
   */
  public StAXSource(final XMLStreamReader xmlStreamReader) {

    if (xmlStreamReader == null) {
      throw new IllegalArgumentException(
          "StAXSource(XMLStreamReader) with XMLStreamReader == null");
    }

    int eventType = xmlStreamReader.getEventType();
    if (eventType != XMLStreamConstants.START_DOCUMENT
        && eventType != XMLStreamConstants.START_ELEMENT) {
      throw new IllegalStateException(
          "StAXSource(XMLStreamReader) with XMLStreamReader"
              + "not in XMLStreamConstants.START_DOCUMENT or "
              + "XMLStreamConstants.START_ELEMENT state");
    }

    this.xmlStreamReader = xmlStreamReader;
    systemId = xmlStreamReader.getLocation().getSystemId();
  }

  /**
   * <p>Get the <code>XMLEventReader</code> used by this
   * <code>StAXSource</code>.</p>
   *
   * <p><code>XMLEventReader</code> will be <code>null</code>.
   * if this <code>StAXSource</code> was created with a
   * <code>XMLStreamReader</code>.</p>
   *
   * @return <code>XMLEventReader</code> used by this <code>StAXSource</code>.
   */
  public XMLEventReader getXMLEventReader() {

    return xmlEventReader;
  }

  /**
   * <p>Get the <code>XMLStreamReader</code> used by this
   * <code>StAXSource</code>.</p>
   *
   * <p><code>XMLStreamReader</code> will be <code>null</code>
   * if this <code>StAXSource</code> was created with a
   * <code>XMLEventReader</code>.</p>
   *
   * @return <code>XMLStreamReader</code> used by this <code>StAXSource</code>.
   */
  public XMLStreamReader getXMLStreamReader() {

    return xmlStreamReader;
  }

  /**
   * <p>In the context of a <code>StAXSource</code>, it is not appropriate
   * to explicitly set the system identifier.
   * The <code>XMLStreamReader</code> or <code>XMLEventReader</code>
   * used to construct this <code>StAXSource</code> determines the
   * system identifier of the XML source.</p>
   *
   * <p>An {@link UnsupportedOperationException} is <strong>always</strong>
   * thrown by this method.</p>
   *
   * @param systemId Ignored.
   * @throws UnsupportedOperationException Is <strong>always</strong> thrown by this method.
   */
  public void setSystemId(final String systemId) {

    throw new UnsupportedOperationException(
        "StAXSource#setSystemId(systemId) cannot set the "
            + "system identifier for a StAXSource");
  }

  /**
   * <p>Get the system identifier used by this
   * <code>StAXSource</code>.</p>
   *
   * <p>The <code>XMLStreamReader</code> or <code>XMLEventReader</code>
   * used to construct this <code>StAXSource</code> is queried to determine
   * the system identifier of the XML source.</p>
   *
   * <p>The system identifier may be <code>null</code> or
   * an empty <code>""</code> <code>String</code>.</p>
   *
   * @return System identifier used by this <code>StAXSource</code>.
   */
  public String getSystemId() {

    return systemId;
  }
}
